This project examines the initial interaction of Mycobacterium avium- intracellulare complex (MAC) with host cells. Primary infection by MAC, either through the gastrointestinal or the respiratory tract requires transepithelial passage. However, during established infection organisms are found almost exclusively in macrophages. Therefore, MAC interaction with both epithelial cells and macrophages will be examined. Preliminary data show that Mycobacteria are recognized and ingested by epithelial cells primarily through interaction of both the pathogen and the host cell with fibronectin. Further preliminary data show that macrophage uptake of Mycobacteria also is markedly influenced by fibronectin. In this project, the role that fibronectin has for MAC uptake by both epithelial cells and macrophages will be determined. Whether mannose/fucose receptors, implement receptors, IgG Fc receptors, or the beta2 family of integrins have a function in MAC phagocytosis by macrophages will be determined. The interactions of MAC lipoarabinomannans and glycopeptidolipids with host cells, and the receptors by which these interactions occur, will be defined. Further experiments will examine the hypothesis that the receptor involved in phagocytosis influences the biochemical characteristics of the MAC-containing phagosome and the ultimate fate of the infection. Whether monocytes and monocyte-derived macrophages from HIV-infected patients use the same mechanisms for MAC phagocytosis will be determined. Preliminary data suggest that cells from HIV-infected patients have decreased surface expression of beta2 integrins. Because of its importance in host cell recognition and phagocytosis, the MAC fibronectin receptor will be purified, its gene cloned and sequenced, and high affinity monoclonal antibodies will be prepared which inhibit MAC infection of cells. Finally, the role for MAC binding to fibronectin in pathogenesis of infection will be tested in a murine model of MAC infection in immunodeficient scid mice. Together, these studies will define completely the receptors involved in recognition and ingestion of MAC by host cells and will test whether interruption of MAC binding to fibronectin can prevent or ameliorate infection.